Abstract

An axial annular‐flow instrument was used to determine the secondary normal stress difference, in case the velocity field is expressed as and The pressure difference, at a fixed axial position, between inner and outer walls of the annulus was measured at various shear rates or axial pressure gradients. The pressure at the outer wall is found to be higher than that at the inner wall throughout the experiment. This means is tensile. The data of pressure difference were analyzed to obtain as a function of shear stress. increases with the square of shear stress at a low shear stress but at a rate slightly less than that when shear stress is above 0.08 MPa or so. Also, is compared with the primary normal stress difference, which had been determined from the measurement of exit pressure with a capillary‐type instrument. The magnitude of relative to is found to be 20–40% for the polymer melts we used.